Suppose you purchased $5,000 worth of furniture and paid back only $3500 before the 90-day deadline. If you are charged 18% simple interest, how much will you s

Question

I have tried to solve using simple interest and partial payments but I am confused. Please help and explain 

Answer 1

I am assuming the interest wasn't charged until after 90 days. So, you owed 5000-3500=$1500 upon which interest was charged.

1500(.18) = $270 interest